For car owners, airbags are our common car safety configuration. This high-tech auxiliary safety device can save the lives of drivers and passengers with great probability in serious traffic accidents.

Perhaps readers don't know that the history of airbags being widely equipped is not too long compared with the invention of automobiles. A bold invention patent in the 1950s had no practical value at that time. However, it was widely used in automobiles after entering the 2 1 century.

It is precisely because of the cooperative use of airbags and seat belts that the possibility of death of drivers and passengers in serious traffic accidents is reduced by 67%, saving the lives of hundreds of thousands of drivers and passengers every year.

In the decades when airbags have not been completely proved to be reliable and practical, a large number of interdisciplinary scientific and technological achievements have gradually infiltrated in the process of continuous research and development, making them a high-tech software and hardware system in automobiles.

Why do I think the airbag system is complicated in structure, exquisite in design and high in technology?

The answer is in this picture, and this issue brings you an analysis of the basic principles of airbags. Similar to the last issue, we will help you understand its working principle comprehensively and thoroughly through intuitive images and practical analysis methods.

In order to avoid the technical content being too complicated, which leads to readers' reading fatigue and unable to fully understand, the author stripped out the seat belt content closely related to the airbag system, and the author can make a special graphic analysis on this content in the future.

What is an airbag system?

The airbag we often talk about actually has an incomprehensible professional name:

Auxiliary restraint system (SRS, auxiliary? Restrain? System).

In fact, the airbag is only one component of the airbag system. Before unifying this name, various manufacturers have given it different professional descriptions, such as air cushion restraint system (ACRS) and auxiliary inflatable restraint system (SIR).

However, they are essentially the same car safety equipment.

In this paper, the well-known airbag system will be used instead of its formal name "auxiliary restraint system".

The airbag system is the most important subsystem in the passive safety system of automobiles. Its main purpose is to restrain and cushion the occupant's body after the collision between the vehicle and the seat belt system, so as to protect their personal safety.

Its working principle is also very simple, which can be vividly described as follows: when a car has a serious collision or rollover accident, the airbag system will start quickly, "blow out" a large soft "airbag" with cushioning function, and cooperate with the restraint function of the seat belt to prevent fatal collision between the driver and passenger and the objects in the car.

According to different functions, airbags are divided into different types and deployed at key positions inside and outside the vehicle. It is not surprising that high-end cars are equipped with airbags above 10.

Diversified classification to ensure safety

Types of airbags

Readers are most familiar with the front airbag on the steering wheel, but in fact, airbag products can be subdivided into many types according to their functions. This section will give you a comprehensive classification and analyze their characteristics one by one.

1. Front airbag

The front airbag is located at the steering wheel and dashboard of the car, which is used to protect the driver and co-pilot passengers in the event of a serious collision. Its protection function is mainly aimed at the strong impact from the front, and this kind of airbag can not provide side and rear protection for passengers.

Because the probability of collision in front of the vehicle is the greatest, the front airbag belongs to the configuration of automobile compulsory equipment in most countries!

You will see its characteristics in the simulation view behind us: because the front airbag works for a very short time and exhausts quickly after deployment, if the vehicle encounters a secondary collision, the airbag will not play any protective role at this time.

Front airbags can be subdivided into driver airbags (DAB) and passenger airbags (PAB).

2. Side airbag (SAB)

Side airbags are generally located in car seats or doors. When the vehicle suffers a strong side collision, the side airbag will pop up quickly and expand in the narrow space between the door and the seat, and this airbag will remain inflated for a little longer.

Its main function is to protect the head or trunk of passengers on this side and prevent them from being injured when they collide with objects in the car.

Side airbags also have their own functions:

Some airbags focus on the side protection of the passenger's chest and trunk, some focus on the side protection of the passenger's head, and some airbags have both functions.

Some well-designed side airbag components can also provide cushioning with different hardness according to the physiological characteristics of different parts of the human side.

For the passenger's relatively soft pelvis and abdomen, the airbag provides a soft cushion, while for the rib-protected chest, the airbag provides a heavy cushion!

Classification of airbags

3. Side curtain airbag (cab)

Side curtain airbags are generally arranged in the interior trim panel above the door, so they are named after being unfolded into a thin tube and covering the whole window, which looks like curtains.

It not only reacts to collision, but also some products are very sensitive to vehicle overturning. When the above two situations occur, the side curtain airbag will deploy rapidly from top to bottom, focusing on protecting the passenger's head.

In various side collisions and rollover accidents, side curtain airbags can reduce the death rate of passengers with severe brain injuries by 45%.

Compared with the front airbag, this type of airbag can not only keep inflated for a long time, but also have a wider protection range. Some models can even provide lateral protection for up to three rows of passengers!

Side curtain airbags are usually used in conjunction with the above-mentioned side airbags.

(The following types of airbags are generally equipped on mid-to high-end models)

4. Knee airbag (KAB)

With the increasing demand of users for airbag systems, products that provide more comprehensive protection for drivers and passengers are gradually equipped with automobiles.

When the engineers made statistics on long-term collision tests and traffic accidents, they found that although the front airbags can protect the trunk and head of passengers well, serious collisions almost always cause serious injuries to the knees of the victims!

The knee airbag is generally deployed at the front instrument panel, and its main function is to prevent the collapsed instrument panel from squeezing the knees of passengers seriously when the front of the vehicle is seriously deformed.

5. Central airbag

The central airbag can be inflated and deployed in the middle of the car to prevent passengers from colliding with each other due to violent collision.

6. Seat belt airbag

The seat belt airbag is arranged on the seat belt, and its main function is to expand the contact area with the occupant's body when it is activated and deployed, cushion the huge pulling force generated after the seat belt is tightened, and prevent the occupant from being seriously strangled by the seat belt.

7. Pedestrian airbags

Pedestrian airbag is an airbag product that only appeared in recent years, and it is only equipped on high-end luxury models. It does not protect the safety of drivers and passengers in the car. Its main function is to reduce the physical injury of motor vehicles and pedestrians when they collide.

Main components of airbag system

The airbag system is mainly composed of three parts, namely, airbag control unit, sensor and airbag module.

A brief understanding of the basic knowledge of this section will help readers to easily read the simulation demonstration content that will be presented later.

1. airbag control unit (ACU)

Physical airbag computer

Airbag control unit (ACU), commonly known as airbag computer, consists of computer processor, memory and input/output module, and is the core control component of the whole airbag system.

This "brain" software programming algorithm will make a logical judgment according to the information transmitted by the relevant sensors, and finally decide whether to trigger the airbag.

In addition, the airbag computer also provides backup power service for the system, which can self-diagnose the whole system at any time. When there is a fault inside the system, the details of the fault will also be recorded and the user will be warned by the fault light.

Of course, the airbag computer is also responsible for sending relevant data to other in-vehicle systems.

2. Sensor

The information collected by various sensors with different functions in airbag system is the important basic data that airbag control computer must rely on when making decisions.

According to different functions, various sensors are deployed in different positions of the car. In order to ensure that the airbag will not pop up by mistake, the airbag computer logic program will not trigger the airbag to pop up because of the collision information transmitted by a single sensor!

The following lists several sensors that the mainstream airbag system must have (advanced airbag systems use more sensors, and the author will analyze them for you later):

Although the functions of the old and new sensors are slightly different, the common goal of all sensors, without exception, is to convert the detected physical motion characteristics of vehicles into electrical signals and quickly transmit them to the airbag control computer.

◥ airbag system ACU and sensor

① External collision sensor

As the most direct collision sensing component, external collision sensors are arranged at the key contour positions of the front, rear and side of the vehicle.

② acceleration sensor

Sensors are usually installed in cars, which detect the change of acceleration by measuring the inertial displacement of small internal mass and convert its motion characteristics into electrical signals.

For example, frontal collision will cause rapid deceleration, and side collision will cause rapid acceleration.

③ Gyroscope sensor

Gyroscope sensor measures the direction change caused by vibration (such as uncontrolled rotation of vehicle), converts the motion characteristics into electrical signals, and outputs them to airbag computer.

When a vehicle with sensors rolls over, the common signal of the sensor and the acceleration sensor will be defined as a rollover accident by the airbag computer, and the side curtain airbag will be deployed to protect the occupants in the vehicle.

④ Seat occupancy sensor

In early airbag systems, there was no such sensor. The seat occupancy sensor is used to control the deployment of the airbag more accurately. When there are no passengers in the seat, the airbag system will not start!

The sensor is generally deployed in the front seat, and its function is realized by electric pressure sensing.

⑤ Wheel speed sensor

The wheel speed sensor is equipped with the wheel position, and collects the driving speed of the vehicle through electromagnetic signals.

Is the vehicle running and exceeding the minimum speed of airbag activation?

This information is one of the most basic data that airbag computer must refer to for logical operation and judgment!

3. Airbag module

The inflation process of airbag must be fast and accurate.

Therefore, the airbag module is not only an elastic airbag filled with gas, but also has a complex structure. It consists of an inflator and an airbag body.

① Inflating device

◥ Activation process of two inflators? Uniform ignition mode

Although the airbag system is considered as a "passive" safety protection technology, its working principle is actually very "active" and "violent"!

The igniter is made of a resistance wire wrapped with a combustible substance. When the current is switched on, it will cause its high temperature, thus igniting a strong combustible substance.

We can vividly compare it to a miniature "electric detonator", and the whole inflation process is more like an explosive explosion. In fact, the basic working principles of the two are exactly the same.

Please remember this metaphor, which will be used later.

As shown in the above figure, the small-scale explosion of the igniter will puncture the first bursting disc, which will directly lead to the second violent explosion of a large number of highly flammable chemicals (mainly composed of environmental-friendly ammonium nitrate and nitroguanidine) in the inflator. The second stage explosion will produce a large amount of nitrogen, which will then flow into the airbag.

The high-pressure gas makes the airbag expand instantly, break through the container and pop up quickly. Its average deployment time is only 20 milliseconds, and its pop-up speed is nearly 300 km/h!

You know, the blink time of our human beings is about 200 milliseconds, and this unfolding speed can completely build a soft wall for life protection in the early stage of human inertia!

② Airbag body

Structure of airbag body

In order to ensure the airbag can be deployed smoothly when needed, the airbag body is made of anti-aging and high-durability polyamide fabric with low friction coefficient, and the manufacturer also preset lubricating powder (usually talcum powder or corn starch) in it.

This is also the reason why we see white smoke in the cab after the airbag is deployed. Readers, that's not fire!

The airbag body is stored in a narrow airbag module in a tightly folded manner, and the rear structure is reserved to allow gas to escape from the exhaust port for air leakage buffering after the airbag is fully deployed.

Trigger condition

Different types of airbags have different trigger conditions. In order to save space, the author only lists some trigger conditions that need to be understood in the next simulated accident scenario:

Tip: Remember, each individual trigger condition cannot force the airbag computer to make a decision to deploy the airbag!

① speed

Remember the wheel speed sensor we mentioned earlier?

The absolute trigger condition of frontal airbag collision is that the absolute driving speed is about 50 km/h or above (different systems are slightly different).

② Angle

For the simulation case in the next section, the frontal collision sensor we are about to introduce will only be recognized as an effective frontal collision by the system when it collides at an angle of 30 degrees (60 degrees in total) on either side of the vehicle centerline.

③ acceleration

The acceleration sensor we mentioned earlier transmits data for the reference of airbag computer.

The trigger condition is that the absolute value of acceleration during collision is about 40g or more.

Are there any passengers in the seat?

The airbag system equipped with seat occupancy sensor will determine whether the airbag needs to be opened according to whether there are passengers in the seat.

Of course, at present, the triggering algorithm of automobile airbag becomes more complicated. The more high-end multi-airbag models, the more detailed the data that needs comprehensive measurement. This section only lists a few exemplary trigger conditions, so that readers can understand the principle more thoroughly.

Best cognitive style

Simulation demonstration of airbag system

After understanding the contents of the previous chapter, let's look at the dynamic simulation animation of airbag system made by the author. I believe everyone can understand its working principle intuitively and systematically.

◥ Typical frontal collision traffic accident? Dynamic diagram of airbag system working simulation

In this "accident", due to improper operation by the driver, the right front side of the car hit the highway guardrail.

At the moment of collision, due to the violent collision, the right front collision sensor took the lead in responding. At the same time, wheel speed sensor, acceleration sensor, seat occupancy sensor and other related components also send their captured data back to the airbag computer.

A large number of basic data are collected in the airbag computer processing queue, and the computer chip makes a logical judgment according to these real-time basic data and the operating rules preset by the manufacturer. The author gives a vivid and simple formula:

① Speed condition (√)+② Angle condition (√)+③ Acceleration (√)+④ Whether there are passengers on the seat (√) = Deploy the front driver airbag immediately (calculation result).

The airbag computer immediately sends activation and deployment instructions to the airbag at the designated position. Remember the "electric detonator" that the author told you to remember?

A small explosion will cause another larger deflagration. . . . . .

It's that simple!

Through the foundation of the above-mentioned basic knowledge, there is no need to use many languages to analyze this link that truly simulates the working principle of airbags.

You should not only know how the components in the whole system work together, but also know the internal working details of each component (such as how the airbag is deployed)!

Tip: Sometimes, when we have a traffic accident, the airbag will not deploy. After reading this graph, you will have the concept of trigger condition in your mind.

Sometimes, it is not the fault of the vehicle, but the collision result cannot constitute the comprehensive trigger condition for airbag deployment.

Practical advice for readers

The following are some practical suggestions on airbags summarized by the author according to the bad habits of domestic car owners (limited to space, this article will not be analyzed, but will reply to comments and exchanges):

1. The co-pilot position must not be used by children (even if there is a child safety seat, it must be prohibited);

2. The position where the airbag pops up is not allowed to be blocked by anything, including some fancy instrument table mats, inferior seat covers, curtains, etc.

3. In principle, all airbag components are not allowed to be repaired, that is, they are only replaced without maintenance;

4. Try not to adjust the seat too far when driving, and keep the steering wheel at a certain distance from the chest;

5. Readers who like extreme cross-country activities, please turn off the airbag system before participating in such activities (some hard-core SUVs and pickups have this function switch. Vehicles without this function can be turned off manually);

6. When the airbag fault light is on, seek maintenance support as soon as possible.

Information from the author

The safety performance of cars has become the primary consideration for a considerable number of consumers to buy cars, and the airbag system can also reflect the overall safety of cars from the side.

The airbag system in this illustrated example is only a medium-level and more advanced airbag system configuration, which not only has more airbags and sensors, but also requires more complex and precise logic algorithms of the airbag computer.

At present, some advanced airbag systems have been developed to intelligently control the deployment strength of airbags according to the specific physical conditions of drivers and passengers at the moment of accident, so as to protect drivers and passengers to the maximum extent.

But no matter from which aspect, the airbag belongs to the auxiliary restraint system, which also proves that it is only an auxiliary safety means. If you don't wear a seat belt, its protective performance will be greatly reduced or even completely ineffective!

In addition to traffic accident casualty statistics, the author only gives the most direct reason: in the long-term practice evolution of airbags, there is a branch of theoretical practice, which is to expect to completely replace uncomfortable seat belts, but the final result is a complete failure!

So remind readers that even the advanced airbag system of the most upscale models may not save your life in a serious traffic accident if you don't wear your seat belt!

I wish readers a pleasant journey and a safe journey!

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.